For a long time, botanists were puzzled by the ability of many plants to defy the laws of science. One wondered how a plant could grow to be over 33 feet tall. To understand the miracle, some basic knowledge of broken rules is necessary.
Atmospheric pressure at sea level and room temperature are less than 15 pounds per square inch. This pressure is exerted on all objects equally. However, some liquids have high surface tension. The molecules stick together. When the end of a small tube is inserted into a container of water, the air pressure on the water in the container causes the water in the tube to rise. The tighter the tube is squeezed, the more the water will increase.
It is the basis of how the original barometer works.
This process, called capillary action, was once remembered as how plants transport water from the roots to the highest point of the plant.
However, botanists soon realized that this idea needed to be fixed. Even with a small diameter pipe, water can only flow so far due to gravity. This natural limit is about 33 feet.
Capillary action explains how a plant, such as a tomato, transports water from the roots to the upper leaves. However, it does not explain how many 33-foot tall trees receive water upward. If capillary action were the explanation for how water is transported to the top of all plants, no tree should be able to reach a height of 33 feet. Therefore, it would be a violation of the laws of nature.
Capillarity works like a gravity pump pushing water down a pipe. It does not explain why a plant can be over 33 feet tall. However, water only flows to the leaves and back to the roots. Instead, plants have tiny pores in their leaves through which water evaporates from the leaf surface. This process is called transpiration. It works similarly to transpiration but is different from sweating.
It also explains how a plant can reach more than 30 meters: this is the limit within which water can be pushed up by the gravity pump of the plant's small tubes. In other words, instead of pumping or pushing water upwards, the plant pulls it upwards by transpiration.
It is partly due to the enormous surface tension of the water. The other part is related to gravity, but differently. This gravity is used in capillary action.
Water evaporates from the leaves in the canopy of a large tree, creating a partial vacuum in the plant's transport system. When the water tries to bind, this gravity drop in the plant's transport tubes pulls the water upward from below. The pressure difference is also enormous. The force pushing the water upward in the transport tubes is several times greater than the force of gravity driving the capillary pumps. It equates to a pressure of more than 1,000 pounds per square inch.
Although the transpiration mechanism is straightforward, it allows plants to grow over 33 feet tall. Coast redwoods, for example, can exceed 1,000 feet in height. More interestingly, plants have been using this system for a long time, much longer than it has taken humans to figure out how to do the same thing.
We often refer to a person without a brain as a vegetable. When we say this, we insult the vegetable.
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